Warning, warning: The latest Snow Leopard bug seems to threaten all your data, and it seems back-up has become essential, while Apple explores if the bug is just an isolated outbreak or a more serious matter.

There’s been a series of complaints across the last month of incidents in which users start their Macs up as normal only to find they’ve logged in as ‘Guests’ on their machine – with all the files and data held on their Mac in their own user account seemingly deleted.

A series of posts on Apple’s Discussion forums presently describe the problem. Here’s one description taken from these: “A day before the crash there was no Guest account folder in the /Users directory. Just prior to the crash a Guest account folder appeared in the /Users directory on my start-up disk (not the partition my home folder is stored on). Post crash that Guest folder has disappeared again.”

Seems the Guest account is created by default.

We’re still sifting through this information, but here’s a link to a Cnet report which may offer some kind of salvation. How to restore Lost home folder after logging in as guest in Snow Leopard. (Good old Cnet, this report was published last month, but we hadn’t heard about it or the problem, so we figured many of you may also benefit from knowing about it.)